1. Field of the Invention
This invention relates to pneumatic tires, and more particularly to an improvement in a shoulder portion of a pneumatic tire having plural lugs defined by notches in each of tread side regions.
2. Related Art Statement
In each side edge region of the tread portion of the tire is arranged either a so-called square shoulder having a substantially squarish section in accordance with the purpose of the tire use.
Even in a pneumatic tire having plural lugs in each side region of the tire tread, the round shoulder or the square shoulder is applied to the side edge of the lug in accordance with the purpose of the tire use.
As is well-known, tires having a so-called round shoulder, wherein an axial end of a lug defined by transverse grooves arranged at a predetermined interval in the circumferential direction of the tire tread exhibits a round shape in the transverse section of the tire, are suitable in the running on general road conditions and can ensure the smooth steering stability, but are lacking in the gripping force in a direction crossing to the running direction of the vehicle due to the absence of gripping against road surface on snow road, muddy road or the like, so that they have still a problem in the straight running property and cornering properties.
On the other hand, tires having a so-called square shoulder, wherein the axial end of the lug exhibits a square shape in the transverse section of the tire, are excellent in the straight running property and cornering properties because the gripping force in a direction crossing to the running direction of the vehicle is strong, so that they are suitable for use on a snow covered road, muddy road or the like. However, when they are run on general road particularly provided with wheel tracks, the lug is apt to be caught by the wheel track and the reaction force accompanied therewith makes the directional control unstable to degrade the straight running property.